The proposed project aims at defining objectively, inside the tooth, the nerve organization which mediates dental pain. Known somatic (pertaining to perceptible stimuli) and autonomic (pertaining to control of involuntary functions) components of the nerves will be structurally and functionally differentiated in order to evaluate the relative contribution of each. The results will end classical controversies concerning functionally defined nerve elements in the tooth pulp and the predentine. Emerging data will provide the basis for a unique and objective structure-function concept of the nervous pain receptor in the tooth. This concept can be directly applied, through existing relevant tests, to dental pain in man. The project will contribute to knowledge in the field of pain mechanisms in general. The proposed experiments require collaboration between laboratories with competent investigators to perform special techniques, i.e. electro-physiology of tooth nerves at the Department of Physiology, University of Bristol, England and three-dimensional and quantitative electron microscopy of nervous structures in the Ultrastructure Laboratory, College of Dentistry, University of Iowa. Bristol supports its own part of the project. The methods include: 1) recording of electrical nerve activity in feline, mandibular teeth, 2) total and selective nerve sections of trigeminal and/or sympathetic supplies with electrophysiological control, 3) three-dimensional reconstruction of normal and surviving nerve structures using electron microscopy at the receptor level and 4) quantitation of normal and surviving nerve structures using electron microscopy at the level of the intradental nerve. Method items 1 and 2 are to be executed in Bristol, items 3 and 4 in Iowa City.